Virtual microphone apparatus and method

Abstract

An apparatus and method for producing an output signal representing a sound pressure at a predetermined position wherein a first microphone is provided for producing a first output signal representing a sound pressure P 0 at a first position; a second microphone is provided for producing a second output signal representing a sound pressure P 1 at a second position; and a signal processing circuit is provided for producing the output signal based upon the first output signal and the second output signal; wherein the signal processing circuit is operative to produce the output signal proportional to: (i) a power function of the second output signal based on an exponent m corresponding to a distance between the first microphone and the predetermined position, multiplied by (ii) a power function of the first output signal based on an exponent representing a value obtained by subtracting at least the exponent m of the power function of the second output signal from 1.

What is claimed is: 
     
       1. An apparatus for producing an output signal representing a sound pressure at a predetermined position, comprising: first microphone means for producing a first output signal representing a sound pressure P 0  at a first position;   second microphone means for producing a second output signal representing a sound pressure P 1  at a second position; and   signal processing means for producing said output signal based upon said first output signal and said second output signal;   said signal processing means being operative to produce said output signal proportional to: (i) a power function of said second output signal based on an exponent m corresponding to a distance between said first microphone means and said predetermined position, multiplied by   (ii) a power function of said first output signal based on an exponent representing a value obtained by subtracting at least said exponent m from 1.     
     
     
       2. An apparatus according to claim 1, wherein said signal processing means is operative to produce said output signal representing a sound pressure at a predetermined position on a line determined by the positions of said first microphone means and said second microphone means such that said output signal is proportional to a value:   P.sub.0.sup.1-m · P.sub.1.sup.m     where m is a ratio of a distance between said first microphone means and said predetermined position to a distance between said first microphone means and said second microphone means.   
     
     
       3. An apparatus for producing an output signal representing a sound pressure at a predetermined position, comprising: first microphone means for producing a first output signal representing a sound pressure P 0  at a first position;   second microphone means for producing a second output signal representing a sound pressure P 1  at a second position;   third microphone means for producing a third output signal representing a sound pressure P 2  at a third position, said first microphone means, said second microphone means and said third microphone means being positioned to produce respective first, second and third output signals representing sound pressures at corresponding positions lying substantially in a common plane;   and signal processing means operative to produce said output signal representing a sound pressure at a predetermined position substantially coplanar with said corresponding positions such that said output signal is proportional to a value:   P.sub.o.sup.(1-m-n) · P.sub.1.sup.m · P.sub.2.sup.n       where m is a ratio whose denominator is a value representing a distance between said first position and said second position along a first line determined thereby and whose numerator is a value representing a distance along said first line from said first position to a position on said first line obtained by projecting said predetermined position onto said first line in a direction based on the first and third positions corresponding with said first microphone means and said third microphone means, respectively, and   n is a ratio whose denominator is a value representing a distance from said first position to said third position along a second line determined thereby and whose numerator is a value representing a distance along said second line from said first position to a position on said record line obtained by projecting said predetermined position onto said second line in a direction based on the first and second positions corresponding with said first microphone means and said second microphone means, respectively.   
     
     
       4. An apparatus for producing an output signal representing a sound pressure at a predetermined position, comprising: first microphone means for producing a first output signal representing a sound pressure P 0  at a first position;   second microphone means for producing a second output signal representing a sound pressure P 1  at a second position;   third microphone means for producing a third output signal representing a sound pressure P 2  at a third position; and   fourth microphone means for producing a fourth output signal representing a sound pressure P 3  at a fourth position outside of a common plane of the first, second and third positions; and   signal processing means operative to produce said output signal representing a sound pressure at a predetermined position other than the first through fourth positions such that said output signal is proportional to a value:   P.sub.0.sup.(1-m-n-h) ·P.sub.2.sup.n · P.sub.3.sup.h       where m is a ratio whose denominator is a value representing a distance between said first position and said second position along a first line determined thereby and whose numerator is a value representing a distance along said first line from said first position to a position on said first line obtained by projecting said predetermined position onto said first line in a direction based on the first, third and fourth positions;   where n is a ratio whose denominator is a value representing a distance between said first position and said third position along a second line determined thereby and whose numerator is a value representing a distance along said second line from said first position to a position on said second line obtained by projecting said predetermined position onto said second lien in a direction based on the first, second and fourth positions, and   where h is a ratio whose denominator is a value representing a distance between said first position and said fourth position along a third line determined thereby and whose numerator is a value representing a distance along said third line obtained by projecting said predetermined position onto said third line in a direction based on the first, second and third position.   
     
     
       5. The apparatus according to claim 1, wherein said signal processing means is operative to process said first output signal and said second output signal in digital form. 
     
     
       6. An apparatus according to claim 1, wherein said signal processing means includes: first logarithmic function means for producing a first logarithmic signal representing a logarithm of said first output signal;   first multiplying means for producing a second logarithmic signal representing a product of said first logarithmic signal and a coefficient (1-m);   second logarithmic functions means for producing a third logarithmic signal representing a logarithm of said second output signal;   second multiplying means for producing a fourth logarithmic signal representing a product of said third logarithmic signal and a coefficient (m);   adding means for producing a summation signal representing a summation of said second logarithmic signal and said fourth logarithmic signal; and   inverse logarithmic function means for producing said output signal representing an inverse logarithmic function of said summation signal.   
     
     
       7. A method of producing an output signal representing a sound pressure at a predetermined position, comprising the steps of: providing a first microphone means for producing a first output signal representing a sound pressure P 0  at a first position;   providing a second microphone means for producing a second output signal representing a sound pressure P 1  at a second position; and   producing said output signal proportional to:   (i) a power function of said second output signal based on an exponent m corresponding to a distance between said first microphone means and said predetermined position, multiplied by   (ii) a power function of said first output signal based on an exponent representing a value obtained by subtracting at least said exponent m from 1.